Loop antennas, including arrays involving orthogonally and otherwise relatively positioned or crossed loops have been used for many years in myriads of radio location and homing systems.
For purposes such as the above mentioned reception of radio navigation signals and the like, specifically Loran-C type transmissions, however, resort has been had to the use of linear antennas, such as whip antennas and the like, wherein, unlike loop antennas, all the received signals travel a single path into the receiver front end, with time difference measurements of signal arrival from two or more navigation transmitters unaffected by variations in receiver delays.
When using whip and similar antennas in applications such as vehicle tracking, signal losses caused by buildings in cities and other similar obstructions as well as E-field interference effects, as from the power lines and P-static effects, deleteriously plague the receiving system. Whip antennas, furthermore, for such usages, require considerable length and also the provision of a around plane, neither of which is desirable for vehicle mounting and unobtrusiveness.
Heretofore, while loop antennas obviate these particular requirements and, in addition, do not suffer E-field of P-static interference effects, they have not lent themselves to Loran-C and similar location signal tracking applications in view of their lack of omni-directivity, carrier phase inversion characteristic, the need for a pair of separate loops and associated band-pass filters and low noise amplifiers, and the inherently low signal strengths that may be involved.
An effective method of solving, the omni-directivity problem is described in copending application of Megapulse, Inc., the common assignee herewith, Ser. No. 08/695,361, filed Aug. 9, 1996, for "Method of and Apparatus For Position Location And Tracking Of A Vehicle Or The Like By The Reception At The Vehicle Of Pulsed Radio Navigation Signals As Of The Loran C Type And The Like, With an Autonomous Loop Antenna Receiver".
In my further copending application Ser. No. 733,296, filed Oct. 17, 1996, for "Magnetic Crossed-Loop Antenna", apparatus is described that addresses solving the problems arising from the use of two separate loops with associated circuitry and the low signal strength, enabling greatly improved reliability of reception of Loran C and similar radio navigation transmissions and without the necessity for long antennas or ground planes.
This is achieved by apparatus having, in combination with a pair of orthogonally crossed loop antennas, a corresponding pair of receiver channels for processing the radio signals received by the responsive antennas from radio transmitting stations; means for rapidly switching each loop antenna back and forth between its channel and the channel of the other loop antenna and for selecting the antenna channel with the stronger signals therein, and means for providing, optimum signal-to-noise ratio and sufficiently wide bandwidth in the receiving of the stronger signals in the selected antenna channel to ensure reception time delay stability.
The present invention is primarily directed to providing a ferrite crossed-loop antenna particularly suitable for the above purposes and of optimal performance geometry, compatible, also, with convenient packaging therewith of the receiver and display equipment, also involving a novel method of forming, such structures.